A hot wire anemometer for cryogenic hydrodynamic experiments

A hot wire anemometer using superconducting thin films has been developed for measurements in a gaseous⁴ He turbulent round jet around 4K. Localized velocity fluctuations, down to a few microns, and high frequency events, up to 1 MHz can be detected giving access to the study of turbulent subsonic flow with Reynolds numbers ranging up to 10⁶. First data analysis featuring the energy cascade in this ideal system are also discussed.     

Empirical expression for hot wire with corrections for temperature drift

In using the empirical expression of King's law,E ² =E ₀ ² + BU, to correlate the data obtained from constant temperature hot wire in real low turbulence flow, the value of exponentn can assume widely differing values and is never a universal constant. Also corrections must be employed for varying ambient fluid temperature from the temperature at which calibration was carried out.This paper discuss the possibility of replacing King's law by another empirical expression,E ²=E ₀ ² + BU ^0.5 + CU, in which the exponentn will be fixed at a value 0.5 and the termCU is regarded as a correction factor for changing the exponentn in King's law as well as for the effect of ambient temperature drift.The advantages of using the new expression, beside incorporating the required corrections, are reflected on reducing the errors in local sensitivity resulted from using approximated exponent in King's law, and its validity for very low mean velocities.

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Empirische Formel für den Hitzdraht mit Korrekturen für Temperaturänderungen

Zusammenfassung Benützt man den empirischen Ausdruck des Kingschen Gesetzes,E ²=E ₀ ² + BU ⁿ , um die Meßwerte eines Konstanttemperatur-Hitzdrahtes bei sehr niedriger Turbulenz zu korrelieren, so kann der Wert des Exponentenn sehr unterschiedliche Werte annehmen und ist nie eine universelle Konstante. Es müssen auch Korrekturen angebracht werden, wenn die Fluid temperatur von der Temperatur abweicht, bei der der Hitzdraht geeicht wurde.Dieser Aufsatz diskutiert die Möglichkeit, das Kingsche Gesetz durch eine andere empirische Formel,E ²=E ₀ ² +BU ^0.5 +CU, zu ersetzen, in der der Exponentn zu 0,5 festgelegt wird und in der der AusdruckCU als Korrekturfaktor für den sich ändernden Exponentenn in dem Kingschen Gesetz und auch für den Einfluß abweichender Umgebungstemperatur betrachtet wird.Die Vorteile dieser neuen Formulierung mit den vorgeschlagenen Änderungen liegen in der Reduzierung von Fehlanalysen bei örtlich besserer Empfindlichkeit und in der Gültigkeit des Ansatzes auch für sehr niedrige Geschwindigkeiten.

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Nomenclature B slope of the best fit line which relatedE ² andU ^0.5 - C correction factor in equation (3) - C _l correction factor for temperature drift - C _E correction factor for same output voltage - C _s correction factor for same sensitivity - C error in correction factor - E output voltage of hot wire, volt - E _a output voltage atT _a , volt - E _c output voltage atT _c , volt - E ₀ extrapolated value whereU=zero, volt - r.m.s. for voltage fluctuations, volt - n exponent in King's law - n error in exponentn - Re Reynold's number - S local sensitivity=dE/dU - T _a fluid temperature,^°C - T _c fluid temperature during calibration,^°C - T _w hot wire temperature,^°C - T T _a -T _c ,^° CU mean velocity, m/s - r.m.s. for velocity fluctuation, m/s -      

Calibration and use of hot wire probes for steady state measurements in low density flows

In recent years the use of hot wire probes for steady state measurements in low density flows has proved very valuable in extracting information concerning flow properties. In interpreting hot wire measurements in low density flows, it is imperative that the heat loss to the wire supports be accurately taken into account. In the present paper, a detailed analysis and calibration procedures for the direct evaluation of the end-loss correction factors for a moderate aspect ratio hot wire have been set out, and experimental verification done to establish the validity of the technique.     

Effective thermal conductivity of a medium with ellipsoidal particles

The principal components of the effective thermal conductivity tensor, characterizing stationary heat macrotransfer in a dense medium with dispersed ellipsoidal particles of a different material are calculated by a method suggested in [1]. The case of equally oriented ellipsoids and of isotropically distributed ones are considered as examples.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 107–111, January–February, 1974.The author is grateful to Yu. A. Buevich for his interest.     

The static response of a bowed inclined hot wire

The directional sensitivity of a bowed, inclined hot wire is investigated using a simple model for the convective heat transfer. The static response is analyzed for subsonic and supersonic flows. It is shown that the effects of both end conduction and wire bowing are greater in supersonic flow. Regardless of the Mach number, however, these two phenomena have distinctly different effects; end conduction appears to be responsible for reducing the nonlinearity of the response, whereas bowing increases the directional sensitivity. Comparison with the available data suggests that the analysis is useful for interpreting the experimental results.     

Boiling on a straight pin fin with variable thermal conductivity

This work theoretically investigated the thermal performance and stability characteristics of a straight pin fin subject to boiling considering a temperature-dependent thermal conductivity of fin, k=k _sat(1+b(T−T _sat)). Steady-state temperature distribution and the associated fin base heat flow were for the first time analytically found, whose stability characteristics were evaluated by linear stability analysis. A positive temperature coefficient b will raise both the fin's temperature and base heat flow. The corresponding stability for stable fin boiling was enhanced. A negative b results in an opposite trend. The use of a mean thermal conductivity in fin boiling calculations is discussed. Received on 3 November 1997     

A hot wire method for measuring turbulence in transonic or supersonic heated flows

This work presents a method for measuring fluctuating quantities such as temperature or velocity using a constant current hot wire anemometer. The scope of this method has been extended to include not only supersonic flows, but also transonic flows with low Reynolds numbers and transonic or supersonic heated flows. After examining the dependence of the different coefficients of sensitivity to aerodynamic and thermal parameters, the result of the study was applied to a turbulent boundary layer using a suitable processing method.     

材料热传导系数随温度变化函数的反演方法

材料热传导系数的反演是一类典型的热传导逆问题。针对材料热传导系数随温度变化的情况,本文将材料的热传导系数值按温度区间分段离散,建立了通过材料边界点的温度测量来反演各温度区间热传导系数值的遗传算法和伴随方程法。通过典型算例分析和考虑测量噪声、系统噪声的反演计算结果分析表明：所建立的两种反演算法都是可行有效的,受测量随机噪...     

A proposal for thermal conductivity standards with special respect to convection and radiation effects

The influence of convection and especially radiation on measured liquid thermal conductivities is discussed for steady state methods and the transient hot wire method. New radiation and convection free thermal conductivity data are given for a mixture of 90% toluene and 10% ethanol, and for mono-, di-, and triethyleneglycol. The glycols are suitable as thermal conductivity standards for steady state methods and the transient hot wire method.

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Ein Vorschlag für Wärmeleitfähigkeitsstandards unter besonderer Berücksichtigung der Konvektion und Strahlung

Zusammenfassung Für stationäre Meßmethoden und für die instationäre Hitzdrahtmethode wird der Einfluß der Konvektion und der Strahlung auf die gemessene Wärmeleitfähigkeit von Flüssigkeiten diskutiert. Neue strahlungs- und konvektionsfreie Wärmeleitfähigkeitswerte werden für ein Gemisch aus 90% Toluol und 10% Ethanol und für Mono-, Diund Triethylenglycol angegeben. Die Glycole sind als Wärmeleitfähigkeitsstandard sowohl für stationäre Methoden als auch für die instationäre Hitzdrahtmethode geeignet.

     

Propagation of a combustion wave in a medium with nonlinear thermal conductivity

A study is made of the problem of the propagation of a thermal wave sustained by an exothermic reaction in a perfect gas. It is assumed that the exothermic reaction begins as a result of the heating of the matter in the medium by the thermal wave.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 184–188, July–August, 1979.I thank V. A. Levin for interest in the work.     

Model for predicting effective thermal conductivity of composites with aligned continuous fibers of graded conductivity

Governing differential equations in both transverse and longitudinal directions for predicting the effective thermal conductivities of composites with aligned, graded continuous fibers are derived. It is shown that the effective conductivities of composites with graded fibers are predicted by solving the equations. The results by the present approach are applicable to both dilute and non-dilute cases without additional procedures unlike other approaches. The results are compared with those in the literature, and the applicability of the present approach is justified. A solution by the present approach is obtained analytically or numerically as long as thermal conductivity profile of fibers is given.     

Solution of the inverse problem of thermal conductivity for a melting slab with entrainment

This article proposes an approximate solution to the inverse problem of the Stefan type for a finite region with arbitrary boundary and initial conditions. A comparison with exact solutions is made.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 132–137, May–June, 1973.     

Transient multiboiling in a pin fin with temperature dependent thermal conductivity

Transient heat conduction in fins undergoing different kinds of convective processes (film, transition, nucleated boiling and natural convection) as in multiboiling processes take place, is a strongly non-linear problem because of the abrupt changes in the heat transfer coefficient that occur at certain temperatures. Transient equations for the thermal fields and fluxes are solved simultaneously, giving the time constant of the process; the stationary solution is compared with the numerical or experimental values of other authors. Temperature dependencies of the heat transfer coefficient and the thermal conductivity is assumed due to the large interval of temperatures occurring. Network Simulation Method is used for the numerical solution, which gives simultaneously thermal field of temperatures and heat fluxes.     

The non-isothermal elastic dumbbell: A model for the thermal conductivity of a polymer solution

In a flowing polymeric liquid, molecular orientation will give rise to anisotropic conduction of heat. In this paper, a theory is presented relating the thermal conductivity tensor to the deformation history of the fluid. The basis of this theory is formed by the Hookean dumbbell. It is shown that the anisotropy of the thermal conductivity is proportional to the polymer contribution to the extra-stress tensor. This stress-thermal law makes it relatively simple to incorporate anisotropic heat conduction into the numerical simulation of a flowing polymeric liquid.     

Steady-state thermal waves in the free-stream flow of an ideal gas with a temperature-dependent thermal conductivity

The structure of the stationary transition layer in a cold ideal gas impinging on a heated permeable surface (lattice) is investigated. Hysteresis occurs in establishing the structure of the stationary transition layer.     

Numerical study on a vertical plate with variable viscosity and thermal conductivity

Free convection over an isothermal vertical plate immersed in a fluid with variable viscosity and thermal conductivity is studied in this paper. We consider the two-dimensional, laminar and unsteady boundary layer equations. Using the appropriate variables, the basic governing equations are transformed to non-dimensional governing equations. These equations are then solved numerically using a very efficient implicit finite difference scheme known as Crank–Nicolson scheme. The fluid considered in this study is of viscous incompressible fluid of temperature dependent viscosity and thermal conductivity. The effect of varying viscosity and thermal conductivity on velocity, temperature, shear stress and heat transfer rate are discussed. The velocity and temperature profiles are compared with previously published works and are found to be in good agreement.     

A network theory for the thermal conductivity of an amorphous polymeric material

A model to relate the thermal conductivity tensor to the deformation of an amorphous polymeric material above the glass transition temperature is presented. The basis of the model is formed by the transient network theory for polymer melts. With this theory it is possible to calculate the average orientation of the macromolecular segments as a function of the history of the deformation. Combined with an expression which relates the thermal conductivity to the orientation of the molecules, this provides us with the information needed to calculate the heat conduction tensor. Despite the fact that the simplest possible network model is chosen, there is good agreement with the sparse, experimental results.     

The dynamic calibration of a hot wire by means of a sound wave

Hot wires of various design, operated by the constant resistance method, were calibrated by means of a plane sound wave of 2500 Hz. This is achieved by locating a small open resonance tube axially in a homogeneous incompressible airflow. Its third harmonic is excitated by superimposing a coaxial, damped, progressive, plane wave on the main airstream. The hot wire to be calibrated is situated in an anti-node of the particle velocity. The amplitude at this station is known from the pressure gradient of the standing wave measured at two small holes in the wall by a probe microphone. This device in turn is calibrated in a specially developed “pistonphone”. Numerical results of the diverse designs are communicated; an absolute accuracy of ±2% is achieved.